The present invention relates to light-sensitive compositions containing a novel compound which generates free radicals when it is irradiated with light (hereunder referred to as "light-free radical generator") and more particularly to light-sensitive compositions containing a novel light-free radical generator in which a moiety capable of absorbing light (hereunder referred to as "light absorbing moiety") and an active moiety capable of generating free radicals (hereunder referred to as "free radical generating moiety") through an interaction with the light absorbing moiety when the latter absorbs light and is excited are chemically bonded to one another.
There have been well known, in the field of graphic arts, compounds which are decomposed to generate free radicals when they are exposed to light. These compounds have widely been used as photopolymerization initiators in photopolymerizable compositions; photoactivators in free radical photographic compositions and photoinitiators for reactions which are catalized with an acid generated by the action of light. There have been produced various kinds of light-sensitive materials useful in image-forming systems such as printing, replicating and copying systems using such free radical generators.
To date, commonly used as such free radical generators in various industrial fields are, for instance, aryl alkyl ketones such as benzoin ethers, diethyl acetophenone, oxime esters, acylphosphine oxides, diaryl ketones such as benzophenone, benzil, quinones and bisimidazoles.
These free radical generators are detailed in Journal of Radiation Curing, 1987, July, pp. 6-16 and 18-31.
Typical examples of the free radical generators which generate halogen free radicals are carbon tetrabromide, iodoform and tribromoacetophenone and these generators have widely been used. In addition, s-triazine compounds substituted with trichloromethyl groups as disclosed in U.S. Pat. No. 4,619,998 and U.K. Patent No. 1,388,492 have also widely been used.
However, these free radical generators can be decomposed by irradiation with light having a wave length falling within a substantially limited range. More specifically, they are sensitive to light having wave length shorter than that of the principal rays of commonly used light sources, i.e., those falling within the ultraviolet range. In other words, these compounds cannot utilize effectively light having wave length ranging from near ultraviolet to visible region and thus their ability of generating free radicals is very low.
Recently, it has been tried to use visible lasers or near infrared lasers in addition to ultraviolet rays conventionally used. In such a case, free radical generators must be sensitive to these various laser rays.
Moreover, there have been investigated a method for substantially increasing sensitivity of light-sensitive materials and a method for forming images using a laser, and some methods such as UV projection exposure methods, methods of direct plate-making in which a laser is used, laser facsimile methods and holography have already been practically used. Thus, light-sensitive materials having high sensitivity have correspondingly been developed. To develop such highly sensitive light-sensitive materials, it is essential to find out or synthesize compounds which can effectively generate free radicals when irradiated with light having wave length ranging from near ultraviolet to visible region or further to near infrared region. Many attempts have been directed to the generation of free radicals with light having wave length ranging from near ultraviolet to visible region or further to near infrared region. All these attempts comprise adding, to light-sensitive materials, a combination of an activator capable of generating free radicals and a certain kind of light absorber.
For instance, in U.S. Pat. No. 3,652,275, chalcone type or dibenzylacetone type compounds are used as light absorber and bisimidazole compounds as activators capable of generating free radicals. Moreover, in U.K. Patent No. 2,020,297, merocyanine compounds are used as light absorbers and diphenyl-iodonium salts as activators. In Japanese Patent Un-examined Publication (hereunder referred to as "J. P. KOKAI") No. Sho 58-40302, thiopyrylium salts are used as light absorbers and trichloromethyl substituted-s-triazine compounds as activators; J. P. KOKAI No. Sho 57-21401 discloses a combination of dialkylamino-stilbene compounds as light absorbers and bisimidazole compounds as activators; and in J. P. KOKAI Nos. Sho 54-95687 and Sho 54-151024 and U.S. Pat. No. 4,481,276, merocyanine compounds are used as light absorbers and trichloromethyl substituted-s-triazine compounds as activators.
Moreover, ketocoumarin is used as a light absorber and N-phenyl glycine is used as an activator in "Polymer Engineering and Science", 1983, 23, p. 1022.
Other examples of such light absorbers and activators are disclosed in D. F. Eaton, "Advances in Photochemistry", 1987, 13, pp. 427-487. Specific examples of the light absorbers are acridinium dyes such as acriflavine; xanthene dyes such as Rose Bengale; and thiazine dyes such as Thionine and Methylene Blue, and specific examples of the activators are amines such as triethanolamine, hydrazine and triphenylamine; phosphorus compounds such as triphenyl phosphine and tri-n-butyl phosphine; sulfinic acids such as sodium p-toluene-sulfinate; sulfonic acid esters such as methyl p-toluene-sulfonate; heterocyclic compounds such as oxazole and imidazole; enolate compounds such as dimedone; tin compounds such as tributylbenzyl tin; arylthiourea and N-phenyl glycine.
Other examples of such light absorbers and activators are disclosed in U.S. Pat. Nos. 4,743,529 and 4,743,530.
Systems comprising these activators to which light absorbers are added make it possible to generate free radicals when they are irradiated with light having a wave length longer than that of light conventionally used and it has been tried to use light-sensitive compositions containing these compounds in a variety of fields. However, the free radical-generating ability of these compounds conventionally proposed is not yet sufficient and it has been required to develop light-sensitive compositions having more improved free radical-generating ability.